Introduction  N₂O、C₂H₆、SF₆ are used as refrigerants or working fluids in Rankine cycle. The critical and physical properties of these refrigerants make them as potential supercritical Brayton cycle fluids.

  Method  By using a self-developed MATLAB program and REPROP physical property database published by the National Institute of Standards and Technology (NIST), thermodynamic analysis of supercritical N₂O (S-N₂O), supercritical C₂H₆ (S-C₂H₆) and supercritical SF₆ (S-SF₆) Brayton cycle was conducted with comparison to supercritical CO₂ (S-CO₂) Brayton cycle. Recompression cycle was selected for study, and a variety of conditions were calcuted with turbine inlet temperature in range of 300~550 ℃, pressure in range of 15~25 MPa, and pre-cooler outlet temperature of 32 ℃ and 47 ℃.

  Result  Thermal efficiency calculation results show that S-N₂O, S-C₂H₆, S-SF₆Brayton cycles all exibit high efficiency, and the efficicy is higher than the coresponding thermal efficiency of S-CO₂Brayton cycle, and the thermal efficiency is always improved with the increase of the inlet temperature of the turbine, but the increase of the pressure does not always increase the cycle thermal efficiency. The increase of the outlet temperature of the precooler leads to a significant decrease in the cyclic thermal efficiency.. Flow calculation shows that the total mass flow rate and turbine inlet volume flow rate of S-N₂O, S-C₂H₆, S-SF₆, S-CO₂ cycle are much higher than steam Rankine cycle with similar parameters, but the turbine outlet volume flow rates of these four supercritical fluids are close to each other.

  Conclusion  S-N₂O, S-C₂H₆, S-SF₆ and S-CO₂ cycle all have potential application value.